How do I queue units?

Good evening. I'm new to the forum so firstly I'd like to take my chance and say that I enjoy fiddling around with construct 2 tremendously. And well here goes my first question,

I have made a few buttons that with which I can spawn new units every three seconds. I click the button and a unit spawns after which I click another button and another spawns.

The units that spawn have a bullet behaviour.

Now I wish to know/learn how I can make it so that units queue up and wait for each other if the need for this arises. So for example one unit is stuck for a moment doing his animation up on hitting a set target, and the next in line awaits the unit to complete before proceeding.

I'd like to add that the unit has to kill the object/other unit that it hits. And the unit that walks into the back of the first unit should not damage it as all units going the same way are supposed to be allies.

Kind regards, RSteen.

Thank you for the replies. Struggling with typing and editing with my phone, I'm used to writing on a desktop and this is quite the small screen. I'm sorry for any inconvenience

Good move adding a title It's always recommended, as well as attaching a .capx C2 file if possible. Finally, you can edit a post rather than adding a new one. Welcome to C2!

Use for each (ordered), choose ascending or descending then pass unit IID as a parameter. Well that's it in general.